A flat-panel CRT display basically consists of an electron-emitting device and a light-emitting device that operate at low internal pressure. The electron-emitting device, commonly referred to as a cathode, contains electron-emissive elements that emit electrons over a wide area. The emitted electrons are directed towards light-emissive elements distributed over a corresponding area in the light-emitting device. Upon being struck by the electrons, the light-emissive elements emit light that produces an image on the viewing surface of the display.
It is generally desirable that the electron-emissive elements be clean during display operation. Contaminants that build up on the surfaces of the electron-emissive elements, especially during display fabrication, act to increase the height and/or width of the electron tunneling barriers. This leads to higher operating voltages for the display. Also, contamination of the electron-emissive surfaces produces emission non-uniformity and leads to emission instability. Degraded display performance, even display failure, is commonly the result.
Liu et al, "Modification of Si field emitter surfaces by chemical conversion to SiC," J. Vac. Sci. Tech. B, March/April 1994, pages 717-721, describes various cleaning procedures applied to silicon electron-emissive elements. As Liu et al points out, electron-emissive elements made of pure silicon are especially reactive chemically. Liu et al starts out with oxide-sharpened silicon whiskers. Some of the silicon whiskers are further sharpened by dry oxidation at 950.degree. C. followed by a hydrofluoric acid etch to remove the oxide coatings.
Prior to performing certain fabrication steps on the silicon whiskers, Liu et al cleans the whiskers at 950.degree. C. in a vacuum to remove oxides and other contaminants. Liu et al also mentions that field evaporation or inert gas sputtering can be employed to clean silicon whiskers. Myers et al, "Characterization of amorphous carbon coated silicon field emitters," J. Vac. Sci. Tech. B, May/June 1996, pages 2024-2029, cleans silicon whiskers in aqua regia.
Other materials besides silicon are attractive for electron-emissive elements. One example is molybdenum. Mousa et al, "The effect of hydrogen and acetylene processing on microfabricated field emitter arrays," Appl. Surf. Sci., 1993, pages 218-221, describes subjecting conical molybdenum electron-emissive elements to a hydrogen plasma. Mousa et al reports that the work function is reduced for molybdenum-emitter tips subjected to the hydrogen plasma. It is desirable to have techniques for cleaning (or conditioning) non-silicon electron-emissive elements, especially electron-emissive elements formed with metals such as molybdenum, in order to improve emission performance.